This invention relates to an electrical material, a process for producing the same, and uses thereof and, more particularly, to a material composition having specific properties of sharply increasing its electrical resistance within a relatively narrow temperature range with increasing a temperature [PTC characteristics (positive temperature coefficient)], i.e., to a PTC composition.
PTC compositions can be utilized in a heater wherein heat generation is ceased when it is raised to a specific temperature; in a PTC thermistor; in a heat-sensitive sensor; and a circuit protection device wherein when a circuit containing a cell or the like exhibits a short the current flowing through the circuit is restricted to a predetermined value or less due to the increase of a resistance value, whereas when its short is released the circuit is restored. Currently, various materials have been developed as the PTC compositions. Heretofore, there have been developed BaTiO.sub.3 having a monovalent of trivalent metal oxide incorporated therein, and polymers such as polyethylene and ethylene-acrylic acid copolymers having electrically conductive particles such as carbon black uniformly dispersed therein.
A process for preparing this PTC composition generally comprises incorporating a necessary amount of carbon black in one or more resins used as polymers and kneading them.
Further, PTC composition is utilized in a PTC device wherein this composition is sandwiched or interposed between metallic electrode plates.
Preferred characteristics of PTC compositions used as the PTC device or the like are a large resistance value at a high temperature (a peak resistance), and a low resistance value at room temperature (a room temperature resistance), i.e., a high ratio of peak resistance to room temperature resistance. Further, it is desirable to increase the spacing between electrodes in order to obtain devices having high safety, and to prevent a short between the electrodes.
However, in the prior art PTC compositions and processes for producing the same, even if the thickness of the PTC composition sandwiched between the electrodes is increased in order to produce devices having high safety, a high peak resistance value in proportion to the thickness is not always obtained. In the case of PTC compositions having a certain thickness or above, the peak resistance value reaches a plateau.